The proliferation of data transport networks, most notably the Internet, is causing a revolution in telephony and other forms of real-time communication. Businesses that have been accustomed to having telephony traffic and data traffic separately supported over different systems and networks are now moving towards so-called “converged networks” wherein telephone voice traffic and other forms of real-time media are converted into digital form and carried by a packet data network along with other forms of data. Now that the technologies are feasible to support it, voice over data transport offers many advantages in terms of reduced capital and operating costs, resource efficiency and flexibility.
For example, at commercial installations, customer premise equipment investments and operating costs may be substantially reduced as most of the enhanced functions, such as PBX and automatic call distribution functions, may reside in a service provider's network. Various types of gateways allow for sessions to be established even among diverse systems such as IP phones, conventional analog phones and PBXs as well as with networked desktop computers.
Thus, the field of telephony is turning away from the traditional use of circuit switches operating under stored program control or under the control of industry standardized intelligent network (IN) call processing. Instead, new service processing architectures (such as the so-called “softswitch” approach) and protocols (like the Session Initiation Protocol or ‘SIP’) have arisen, significantly patterned upon techniques developed for the Internet and other data networks.
Aside from cost considerations, a significant advantage and motivation for this change in service processing is the promise of enhanced new services and faster deployment of services. New packet-switched telephony networks, coupled with the aforementioned new service processing paradigms, are being designed to offer users unprecedented levels of flexibility and customizability.
Even at the periphery of the network, a new generation of end user terminal devices are now replacing the traditional telephones and even the more recent PBX phone sets. These new sets, such as those offered by Cisco Systems, Inc. and Pingtel Corporation, may connect directly to a common data network, via an Ethernet connection for example, and feature large visual displays to enhance the richness of the user interface.
Another significant sign of radical departure from traditional telephony relates to the manner in which destinations are expressed. Rather than using the familiar telephone number to place a call to a particular telephone station, the new paradigm relies upon identifying a party whom one is trying to reach, independent of any particular location or station address (such as a telephone number). The current trend is that this identification is alphanumeric and resembles an e-mail address or URI (universal resourse identifier) as is now commonly used in other types of communication. The new phones described above can “dial” such alphanumeric addresses.
This technique of specifying a party rather than a station ties into another novel aspect of packet-switched telephony, namely that user location is allowed to be very dynamic. By default, a given user may be associated with a particular communications terminal (telephone, mobile phone, pager, etc.) in the traditional sense. In addition, the user may approach one of the newer types of IP phone appliances and register his presence to receive calls at the given phone. Any inbound calls will then go to the most recently registered address. Given this mobility, the identification scheme for destination parties must be decoupled from the addressing of specific terminals. Soon the familiar practice of memorizing a “telephone number” may be obsoleted, or at least supplemented, by alternative symbolic expressions for specifying a given destination party, also known as a “terminating” party.